--创建视图
create view empview
as
select employee_id,last_name,salary
from employees
where department_id80;--查询视图
select * from empview--修改视图
update empview set salary20000
where employee_id179
运行结果 --修改视图
create or replace view empview2
a…
刷ROM是什么意思首先,ROM是由英文Read only Memory的首字母构成的,意为只读存储器。顾名思义,就是这样的存储器只能读,不能像RAM一样可以随时读和写。它只允许在生产出来之后有一次写的机会,数据一旦写入则不可更改。它…
--创建表
create table emp01
as
select * from employees
where department_id in (70,80)--
--创建表
create table emp02
as
select * from employees
where department_id in (80,90)
--查询 --并集
select * from employees
where department_id in (70,80)
union all
se…
--子查询 查询last_name为chen的manager信息select employee_id,last_name
from employees
where employee_id(
select manager_id
from employees
where last_nameChen
)
运行结果 --查询
select employee_id,manager_id,department_id
from employees
where manager_id in(
…